Buggy code:
public class XmlStreamReader extends Reader { private static final int BUFFER_SIZE = 4096 ; private static final String UTF_8 = "UTF-8" ; private static final String US_ASCII = "US-ASCII" ; private static final String UTF_16BE = "UTF-16BE" ; private static final String UTF_16LE = "UTF-16LE" ; private static final String UTF_16 = "UTF-16" ; private static final String UTF_32BE = "UTF-32BE" ; private static final String UTF_32LE = "UTF-32LE" ; private static final String UTF_32 = "UTF-32" ; private static final String EBCDIC = "CP1047" ; private static String staticDefaultEncoding = null ; private Reader reader ; private String encoding ; private final String defaultEncoding ; public static void setDefaultEncoding ( final String encoding ) { } public static String getDefaultEncoding ( ) { } public XmlStreamReader ( final File file ) throws IOException { } public XmlStreamReader ( final InputStream is ) throws IOException { } public XmlStreamReader ( final InputStream is , final boolean lenient ) throws IOException , XmlStreamReaderException { } public XmlStreamReader ( final URL url ) throws IOException { } public XmlStreamReader ( final URLConnection conn ) throws IOException { } public XmlStreamReader ( final InputStream is , final String httpContentType ) throws IOException { } public XmlStreamReader ( final InputStream is , final String httpContentType , final boolean lenient , final String defaultEncoding ) throws IOException , XmlStreamReaderException { } public XmlStreamReader ( final InputStream is , final String httpContentType , final boolean lenient ) throws IOException , XmlStreamReaderException { } private void doLenientDetection ( String httpContentType , XmlStreamReaderException ex ) throws IOException { } public String getEncoding ( ) { } @ Override public int read ( final char [ ] buf , final int offset , final int len ) throws IOException { } @ Override public void close ( ) throws IOException { } private void doRawStream ( final InputStream is ) throws IOException { } private void doHttpStream ( final InputStream is , final String httpContentType , final boolean lenient ) throws IOException { } private void prepareReader ( final InputStream is , final String encoding ) throws IOException { } String calculateRawEncoding ( final String bomEnc , final String xmlGuessEnc , final String xmlEnc , final InputStream is ) throws IOException { } String calculateHttpEncoding ( final String cTMime , final String cTEnc , final String bomEnc , final String xmlGuessEnc , final String xmlEnc , final InputStream is , final boolean lenient ) throws IOException { } static String getContentTypeMime ( final String httpContentType ) { } private static final Pattern CHARSET_PATTERN = Pattern . compile ( "charset=[\"\']?([.[^;<seq2seq4repair_space>\"\']]*)[\"\']?" ) ; static String getContentTypeEncoding ( final String httpContentType ) { } static String getBOMEncoding ( final BufferedInputStream is ) throws IOException { } private static String getXMLGuessEncoding ( final BufferedInputStream is ) throws IOException { } public static final Pattern ENCODING_PATTERN = Pattern . compile ( "<\\?xml.*encoding[\\s]*=[\\s]*((?:\".[^\"]*\")|(?:\'.[^\']*\'))" , Pattern . MULTILINE ) ; private static String getXmlProlog ( final BufferedInputStream is , final String guessedEnc ) throws IOException { String encoding = null ; if ( guessedEnc != null ) { final byte [ ] bytes = new byte [ XmlStreamReader . BUFFER_SIZE ] ; is . mark ( XmlStreamReader . BUFFER_SIZE ) ; int offset = 0 ; int max = XmlStreamReader . BUFFER_SIZE ; int c = is . read ( bytes , offset , max ) ; int firstGT = - 1 ; <START_BUG> String xmlProlog = null ; <END_BUG> while ( ( ( c != ( - 1 ) ) && ( firstGT == ( - 1 ) ) ) && ( offset < ( XmlStreamReader . BUFFER_SIZE ) ) ) { offset += c ; max -= c ; c = is . read ( bytes , offset , max ) ; xmlProlog = new String ( bytes , 0 , offset , guessedEnc ) ; firstGT = xmlProlog . indexOf ( '>' ) ; } if ( firstGT == ( - 1 ) ) { if ( c == ( - 1 ) ) { throw new IOException ( "Unexpected<seq2seq4repair_space>end<seq2seq4repair_space>of<seq2seq4repair_space>XML<seq2seq4repair_space>stream" ) ; } else { throw new IOException ( ( ( "XML<seq2seq4repair_space>prolog<seq2seq4repair_space>or<seq2seq4repair_space>ROOT<seq2seq4repair_space>element<seq2seq4repair_space>not<seq2seq4repair_space>found<seq2seq4repair_space>on<seq2seq4repair_space>first<seq2seq4repair_space>" + offset ) + "<seq2seq4repair_space>bytes" ) ) ; } } final int bytesRead = offset ; if ( bytesRead > 0 ) { is . reset ( ) ; final BufferedReader bReader = new BufferedReader ( new StringReader ( xmlProlog . substring ( 0 , ( firstGT + 1 ) ) ) ) ; final StringBuffer prolog = new StringBuffer ( ) ; String line = bReader . readLine ( ) ; while ( line != null ) { prolog . append ( line ) ; line = bReader . readLine ( ) ; } final Matcher m = XmlStreamReader . ENCODING_PATTERN . matcher ( prolog ) ; if ( m . find ( ) ) { encoding = m . group ( 1 ) . toUpperCase ( ) ; encoding = encoding . substring ( 1 , ( ( encoding . length ( ) ) - 1 ) ) ; } } } return encoding ; } static boolean isAppXml ( final String mime ) { } static boolean isTextXml ( final String mime ) { } private static final MessageFormat RAW_EX_1 = new MessageFormat ( "Invalid<seq2seq4repair_space>encoding,<seq2seq4repair_space>BOM<seq2seq4repair_space>[{0}]<seq2seq4repair_space>XML<seq2seq4repair_space>guess<seq2seq4repair_space>[{1}]<seq2seq4repair_space>XML<seq2seq4repair_space>prolog<seq2seq4repair_space>[{2}]<seq2seq4repair_space>encoding<seq2seq4repair_space>mismatch" ) ; private static final MessageFormat RAW_EX_2 = new MessageFormat ( "Invalid<seq2seq4repair_space>encoding,<seq2seq4repair_space>BOM<seq2seq4repair_space>[{0}]<seq2seq4repair_space>XML<seq2seq4repair_space>guess<seq2seq4repair_space>[{1}]<seq2seq4repair_space>XML<seq2seq4repair_space>prolog<seq2seq4repair_space>[{2}]<seq2seq4repair_space>unknown<seq2seq4repair_space>BOM" ) ; private static final MessageFormat HTTP_EX_1 = new MessageFormat ( "Invalid<seq2seq4repair_space>encoding,<seq2seq4repair_space>CT-MIME<seq2seq4repair_space>[{0}]<seq2seq4repair_space>CT-Enc<seq2seq4repair_space>[{1}]<seq2seq4repair_space>BOM<seq2seq4repair_space>[{2}]<seq2seq4repair_space>XML<seq2seq4repair_space>guess<seq2seq4repair_space>[{3}]<seq2seq4repair_space>XML<seq2seq4repair_space>prolog<seq2seq4repair_space>[{4}],<seq2seq4repair_space>BOM<seq2seq4repair_space>must<seq2seq4repair_space>be<seq2seq4repair_space>NULL" ) ; private static final MessageFormat HTTP_EX_2 = new MessageFormat ( "Invalid<seq2seq4repair_space>encoding,<seq2seq4repair_space>CT-MIME<seq2seq4repair_space>[{0}]<seq2seq4repair_space>CT-Enc<seq2seq4repair_space>[{1}]<seq2seq4repair_space>BOM<seq2seq4repair_space>[{2}]<seq2seq4repair_space>XML<seq2seq4repair_space>guess<seq2seq4repair_space>[{3}]<seq2seq4repair_space>XML<seq2seq4repair_space>prolog<seq2seq4repair_space>[{4}],<seq2seq4repair_space>encoding<seq2seq4repair_space>mismatch" ) ; private static final MessageFormat HTTP_EX_3 = new MessageFormat ( "Invalid<seq2seq4repair_space>encoding,<seq2seq4repair_space>CT-MIME<seq2seq4repair_space>[{0}]<seq2seq4repair_space>CT-Enc<seq2seq4repair_space>[{1}]<seq2seq4repair_space>BOM<seq2seq4repair_space>[{2}]<seq2seq4repair_space>XML<seq2seq4repair_space>guess<seq2seq4repair_space>[{3}]<seq2seq4repair_space>XML<seq2seq4repair_space>prolog<seq2seq4repair_space>[{4}],<seq2seq4repair_space>Invalid<seq2seq4repair_space>MIME" ) ; }

Fix:
String xmlProlog = "" ;